This invention relates to the structure and preparation of a vacuum package containing a microelectronic or sensor device, and, more particularly, to such a package having a locally deposited internal getter.
In the past, infrared sensors have required cooling to cryogenic temperatures on the order of 50-80.degree. K to be operable. New sensors that operate at higher temperatures, and even at room temperature, have recently been developed. Like the cryogenically cooled sensors, the higher-temperature infrared sensors are sealed in a vacuum for operation, to prevent contamination or degradation of the active elements, and to provide thermal insulation from the ambient environment. These sensors are frequently less sensitive than those operating at cryogenic temperatures, but they have the advantage of not requiring a cryogenic cooling device. Consequently, they may be made smaller in size and less expensive than cryogenically cooled sensors.
In a typical application under development, an array of 320.times.240 sensor elements is formed on a substrate. Each sensor element is from about 10-50 micrometers by 10-50 micrometers in size. The array is sealed into a package whose interior is evacuated, with external leads extending from the array. Because no cooling is required, the package may be made small, on the order of 1/2-1 inch.times.1/2-1 inch.times.0.06 inch thick, and the packaged device is significantly simplified as compared with a cryogenically cooled sensor and its package.
The interior of the package must remain evacuated and at low pressure. To accomplish this end, getter material is placed inside the vacuum package and activated, effectively forming a chemical vacuum pump. A getter is a material that, when activated, captures gas molecules in a vacuum. The getter absorbs, adsorbs, and/or physically entraps oxygen and other molecules that are outgassed from the array structure over the life of the product.
In most conventional sensor vacuum packages, the getter is placed into a metal tube that is welded to the side of the vacuum package and then heated to activate the getter. In another approach, the getter is attached inside the package to electrical wires extending through electrical feedthroughs, and an electrical current is passed through the wires to heat the getter material and activate it. These approaches are not feasible for the very small vacuum packages now possible with the room-temperature infrared sensors. There is therefore a need for a design and a technique for implementing that design to provide effective gettering inside a small vacuum package. The need is particularly acute for the room-temperature infrared sensor system discussed above, but is also present for a number of other types of vacuum-packaged devices. The present invention fulfills this need, and further provides related advantages.